Reoviruses provide a well-established experimental model for studies of viral neuropathogenesis. Following primary infection in the intestine, type 3 reoviruses disseminate to the central nervous system (CNS), infect neurons, and cause encephalitis. Viral attachment protein s1 plays a crucial role in each of these sequential pathologic steps. The s1 protein consists of an amino-terminal tail and a carboxy-terminal head. The s1 tail binds sialic acid, whereas the s1 head binds an unidentified receptor. The major objective of the proposed research is to determine mechanisms by which interactions between s1 and cell-surface receptors lead to CNS disease. Two specific aims are proposed to study structural and functional properties of s1-receptor interactions. In Specific Aim 1, domains in s1 that determine the capacity of reovirus to grow in the murine intestine, spread from the intestine to the CNS, and infect CNS tissues will be identified by infecting mice with reovirus particles recoated with chimeric, truncated, and mutant s1 proteins and with mutant viruses that have defined alterations in receptor-binding functions. In Specific Aim 2, a cell-surface receptor for the s1 head will be molecularly cloned by screening a neuronal cDNA library for membrane proteins that confer reovirus binding and infectivity to nonpermissive cells. Domains of s1 head receptors required to bind and internalize reovirus will be identified using chimeric and truncated forms of the receptor in assays of virus binding, internalization, and growth. These studies will establish a framework for understanding reovirus cell-attachment and provide new insights into mechanisms by which viruses select cellular targets to initiate neurologic disease.